The majority of the known and commercially available low-pressure fluorescent discharge lamps are so-called compact fluorescent lamps at present. These lamps are intended to replace incandescent lamps used in a wide field of industry and home applications. In order to provide for a CFL that resembles conventional incandescent lamps, a bulb shaped outer envelope may encapsulate the CFL-s. Main advantages of these lamps are low power consumption and long lifetime. Disadvantageous however in CFL-s is their relatively high price and length dimension. Many configurations have been proposed to solve the length dimension problem. Such solutions include multiple tube arrangements and coiled tube arrangements.
Starting voltage requirement of a low-pressure discharge lamp depends on tube length and/or tube diameter among others. A lamp with a longer tube or smaller tube diameter needs higher starting voltage. The higher starting voltage requirement in turn causes increase in size and cost of ballast components. Longer tubes are required to make higher wattage lamps; tubes with smaller diameter are required for smaller volume lamps. Both demands are driven by the market and environmental needs. Also, due to compatibility reasons, the discharge tubes shall advantageously be accommodated in an outer envelope. Additional means are needed to meet these requirements at the same time.
U.S. Pat. No. 4,523,126 describes a starting aid for shaped discharge lamps. The starting aid is a metal band secured to the discharge tube. The starting voltage reduction largely depends on the location of the starting bands. This feature implies an accurate positioning of the starting bands relative to cathode location. Experiments were conducted in order to prove the effectiveness of the solution described in the above-cited patent when applied to compact fluorescent lamps, but no significant starting voltage reduction could be accomplished. It is believed that the negative result is due to the different lamp geometry and the different filling gas. A further disadvantage of the starting aid according to the cited patent is a loss in light output due to the shielding action of the starting band. Calculating with the preferred width of starting bands, the expected lumen loss is in the range of 2-4 percent. A further drawback is that a conductive part is placed on a touchable portion of the lamp. When the hot cathode hits the wall of the glass tube at the end of the life of the lamp the wall may crack and a current path may be formed to the metallic starting band. Therefore the user of the lamp may be exposed to electrical shock.
U.S. Pat. No. 7,053,553 disclosed a starting aid comprising an electrical connector disposed in the plastic housing of the fluorescent lamp. The starting aid has a first end and a second end. The first end is connected to the means suitable for electrically connecting to the socket. The second end is secured to an end portion of an electrodeless discharge tube leg. At least a part of the electrical connector is formed as a spring. This lamp does not have an outer envelope and the discharge tube is secured in a plastic socket also comprising the starting aid. This starting aid can only be used in connection with a special discharge tube configuration without an outer envelope.
U.S. Pat. No. 6,051,930 disclosed a CFL system including a housing with a base connector, a ballast unit located in the housing and a lamp unit comprising a plurality of straight discharge tube members. The lamp unit is fixed rigidly to the housing and also includes an extended wire connection having, a first end electrically connected to one of the lamp electrodes and a second end located near another point on the lamp unit. This configuration favourably modifies the discharge path within the lamp unit but imposes an electric shock hazard due to the fact that the starting aid is in electrical connection with an electrode of the lamp unit and the lamp has no outer envelope.
The existing compact fluorescent lamps with an outer envelope on the market do not comprise starting aid means. CFL-s equipped with an outer envelope has plastic parts and glue/cement that fixes the discharge tube to the plastic housing. Thus there is a particular need to provide a compact fluorescent lamp with a starting aid which reduces the starting voltage of the fluorescent lamp significantly without decreasing the light output of the lamp and ensures safety against electric shock at the end of the life of the lamp. There is a further need to provide a mechanical support means that serves as a starting aid.